: A fundamental problem in biology is how the germ cells develop and are nurtured by the soma so that they can give rise to the next generation of a species. This occurs largely in the gonads, where germ cells and specific somatic cells create the unique environment necessary for the germ cells to differentiate. Despite the importance of this problem. surprisingly little is known about how the germ cells and somatic cells come together to form a gonad. There are many parallels between gonad formation in Drosophila and in other species. Therefore, we can use Drosophila as a model system for understanding this process. We have discovered a new gene, fear of intimacy (foi), that is required for gonad morphogenesis in Drosophila. Infoi mutants, the cells which make up the gonad form normally but the process of gonad coalescence is blocked. FOl is predicted to be a transmembrane protein, and is a founding member of a new family of proteins conserved from yeast to humans. Interestingly, we have found that the cell adhesion molecule E-cadherin is also essential for gonad morphogenesis. Together, FOI and E-cadherin provide a unique entry point for understanding the molecular events that control the formation of the gonad. To better understand the events of gonad morphogenesis, and how FOl and E-cadherin control this process, we will carry out the following specific aims. In Aim 1 we will conduct a cell biological analysis of gonad coalescence and characterize the cellular interactions that occur during this process. In Aim 2 we will determine how FOl is acting at the cellular level to affect morphogenesis. where the FOI protein is localized and what domains of FOI are essential for its function. In Aim 3 we will analyze the role of E-cadherin in gonad morphogenesis, and determine if FOl and E-cadherin are acting together to mediate this process. The completion of these aims will provide the first comprehensive analysis of gonad morphogenesis in Drosophila and provide insight into the molecular mechanisms that control this process.